Do you remember the first time you rode a bike for the first time without training wheels? Many of us don’t.
While I don’t remember my age, I do remember teaching myself to balance on a bike and riding without help. I would roll down a grass hill and try to pedal without falling over. I fell over quite a bit until it clicked. Then you never forget again.
That’s where the phrase, it’s just like riding a bike came from.
The most uncoordinated person can learn and seemingly never forget.